(1) Field of the Invention
The present invention relates to a novel cathode suitable for generating hydrogen, which is used as the cathode for the electrolysis of sodium chloride, water or the like, and a process for the fabrication of this novel cathode.
(2) Description of the Prior Art
The technique of obtaining chlorine and sodium hydroxide by the electrolysis of an aqueous solution of an alkali metal salt, especially by the electrolysis of an aqueous solution of sodium chloride according to the process using an ion exchange membrane, has recently been advanced, and the electrolysis at a higher current efficiency and a lower voltage, that is, the improvement of the power efficiency, is eagerly desired. Of this technical trend, the improvement of the current efficiency is achieved mainly by improving the ion exchange membrane and the reduction of the operation voltage is achieved by reducing the overvoltage while improving the ion exchange membrane. In connection with the anode, many excellent proposals have already been made, and electrodes in which the problem of the anode overvoltage is of no substantial significance have been used on an industrial scale.
Electrodes formed of soft iron or nickel are industrially used as the cathode, that is, the electrode for generating hydrogen, and since such a high hydrogen overvoltage as about 400 millivolts is allowed in these cathodes, it is pointed out that reduction of this overvoltage is necessary.
Various means for reducing the hydrogen overvoltage have been recently proposed in patent specifications. For example, Japanese Patent Application Laid-Open Specifications No. 164491/80, No. 131188/80, No. 93885/81 and No. 167788/83 propose fine particle fixed type electrodes in which particles of nickel, cobalt, silver or an alloy thereof with aluminum or other metal are fusion-bonded to an electrode substrate, or these particles are embedded in a retaining metal layer formed of silver, zinc, magnesium or tin so that the particles are partially exposed and if desired, a part of the retaining metal layer is chemically corroded to render the metal layer porous. Furthermore, Japanese Patent Application Laid-Open Specification No. 60293/79 proposes a hydrogen generating electrode in which the hydrogen overvoltage is reduced by an active metal electrodeposition process where electro-plating is conducted on an electrode substrate by using a plating solution comprising a sulfur-containing nickel salt.
Cathodes having a relatively small hydrogen overvoltage may be fabricated according to these proposals. However, further improvements are desired for further reducing the overvoltage, increasing the durability of the cathode performance and decreasing the manufacturing cost. For example, the fine particle fixed type electrode is generally defective in that the metal constituting fine particles is expensive, the preparation of fine particles is difficult, the electrode fabrication process is complicated, the deviation of the electrode performance is great and the performance stability is low. Moreover, the electroplating process using a sulfur-containing nickel solution is defective in that it is difficult to sufficiently reduce the hydrogen overvoltage.